In the medical field and the like, there have been proposed various kinds of automatic analyzer. Generally speaking, in the automatic analyzer, a sample is analyzed by mixing a biospecimen such as blood or urine with a reagent to obtain a reaction liquid and by performing automatic measurement thereon. The mixture of the biospecimen with the reagent is generally performed by dispensing the sample and reagent from the sample container and reagent container in predetermined amounts through suction dispensing by using a dispensing apparatus (dispense probe) or the like, and by supplying them to a reaction container for reaction.
When performing the dispensing, the distal end of the dispense probe is put into a liquid substance such as the sample and reagent to be dispensed; the deeper it is put in, the more liquid adheres to the outer wall of the probe, resulting in an increase in contamination between the different samples and reagents. Further, the deeper it is put in, the more time is needed for the vertical movement. In view of this, the height of the liquid surface is detected so that the distal end of the dispense probe may be allowed to enter only slightly, with the distal end of the dispense probe being controlled in height direction in conformity with the height. Regarding the technique for detecting this liquid surface height, there is known the problem of erroneously recognizing the height of the surface of any bubble generated on the surface of the liquid as the height of the liquid surface, resulting in failure in suction. To cope with this problem, there has been examined how to detect the liquid surface condition through image processing.
For example, Patent Document 1 discloses a method in which illumination is applied from above to the object of inspection and in which an image of the liquid surface is taken through imaging by a color camera. Then, reflection (mirror surface reflection) of the illumination on the liquid surface is extracted by utilizing hue information indicating a difference in the ratios of the spectral components of light and is counted to thereby detect the presence of bubbles. It can happen that the reflection light from the bottom surface of the sample container creates various complicated and varied images, and that bubbles not interfering with the suction dispending are generated at the position of the inner wall of the sample container below the liquid surface. In the case, however, by using the method in which the mirror surface reflection of the illumination is extracted, it can be easily distinguished from the condition of bubble generation on the liquid surface.
As another examination example, Patent Document 2 discloses a method in which, after the processing of obtaining the center of a liquid surface circle with respect to the inspection image at the time of imaging by a camera, histogram evaluation and FFT evaluation of a radial image having undergone polar coordinate transformation, and further, ring detection through Hough transformation, are conducted to thereby detect bubbles.